mena661
Southern California
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Normk wrote:
As for the alternator drive, you will need either a poly V belt or at least a double V belt configuration in order to drive a 250 amp alternator. Thanks for posting this. It's much better than saying "you'll have trouble" and not explaining why.
2006 Ford F250 Lariat 6.0 PSD 2WD
2010 Keystone Outback Super-Lite 285FL 5er, Reese Signature Series 18K w/Manual Slider
Four Trojan L16 6V's (740Ah)
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pnichols
Santa Cruz Mountains
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Quote:As for the alternator drive, you will need either a poly V belt or at least a double V belt configuration in order to drive a 250 amp alternator. Having a larger drive surface such as in a poly V or multiple belt set-up will be far superior to trying to achieve enough tension to drive through a single belt.
The only reason to have heavier drive belts on a 250 amp alternator is if you want very heavy currents to be delivered by it.
A 250 amp alternator, with stock/standard drive belts, can also be used to deliver heavier currents than stock generators at engine idle RPMs.
This may be what the OP might be doing most of the time ... idling the main engine to initially and partially charge batteries at say, 70-90 amps .... which would require a 250 amp alternator at idle speeds but using only stock/standard drive belts with standard over-drive pulley ratios.
Phil, 2005 E450 Itasca 324V Spirit
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Normk
Canada's Wet Coast
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The comment regarding the drive required is right on target, it will require the same mechanical power to drive a 250 amp alternator delivering 70 or 90 amps as to drive a 105 amp alternator at the same amperage. One problem, however, in undersizing the drive is in the event that the alternator output attempts to rise above the capacity of the drive. Let's take for example that the alternator's drive (belts) are able to provide sufficient power transfer to turn the alternator with enough torque to deliver 150 amps. All will be well and one will never know the difference unless the alternator attempts to produce 151 amps. At that point the belt will begin to slip, belt will over heat and the alternator rotor will decrease in RPM. The regulator will sense lower voltage and will increase rotor field current which will require even more torque to turn the rotor. The rotor will very quickly come to almost stopped and the belt will burn off.
Unless one has a means to sense output current and so limit alternator output to below the capacity of the drive, this failure will occur. There would be little practical advantage to installing a much larger capacity alternator unless the drive capacity is sufficient.
The point about the 250 amp alternator's ability to produce more output at idle (assuming it is above sufficient RPM) is well taken but this could easily and more practically be overcome by simply turning the smaller capacity alternator at higher RPM.
Please recognize that I am not arguing against pnichols points as they are correct and the scenario presented may point to a practical solution in some cases. Depends what you need to do and how you intend to use the installation.
Thanks for mentioning the higher output (which would be the likely case) at lower RPM as I was remiss in not mentioning that.
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pianotuna
Regina, SK, Canada
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Hi,
I think the larger alternator is a bit of a "red herring". My stock 130 amp alternator came with a 60 amp fused oem house battery charging circuit. I do know I've blown the fuse (twice), and destroyed the oem (cheap garbage, the contacts burned) relay. I have replaced the relay with much heavier duty unit, and gone to an automatic circuit breaker to replace the fuse. I've also added a second charging circuit to double the capacity. I don't have figures right now--but am installing a "hall effect" ammeter in the spring.
By the time he pays for a larger alternator and the necessary mods to the belt system to "make it work" he would be far better off to install solar. Why? Because above about 85% state of charge the stock alternator will do just as well as the 250 amp one, provided the wire size is adequate to the task. With flooded batteries there is no point going over the c/8 rate after 85% has been reached.
We do not know the results of an energy audit. Therefore no one can give more than a wild guess on battery bank size. He may have a lack of storage space, both from a weight and size point of view, so I expect the bank to be "on the small side". If he gets lucky, say 500 amp-hours. That makes c/8 40 amps.
The very first modification I'd make is to beef up the wire in the charging path, including a heavy duty continuous mode relay. If, and when, the oem alternator fails--he could go "up" in size to a 130 amp unit, probably with no modifications to the belt system.
The OP plans to run a generator. He also plans on having 120 volt power in an rv park one day per week. Therefore he needs a decent converter sized to be able to get the battery bank fully charged overnight. As always the last 15% simply takes a lot of time. This argues for a smaller battery bank--say 250 amp-hours. It may also argue for AGM chemistry to "get around" the 85% state of charge "slow down".
In his shoes, I'd go 500 amp-hours of battery bank (AGM?) and 300 watts of solar.
* This post was
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Regards, Don
Kustom Koach Class C 28'5" 256 watts solar, 875 amp hours in two battery banks 12 volt batteries 2500 watt inverter.
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wa8yxm
Wherever I happen to park
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Do you have to worry about the coach batteries charging too quickly.
No, you don't. So long as the REGULATOR is good on the alternator the internal resistance of the battery will limit charging current to a safe level.
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377
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renoman69
Edmonton Alberta
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I am totally with PT on this debate. I would nix the new alternator and upgrade the charge wires. Put a 2 6V Trojans in for now to see how things work. Then do a solar panel or two if I needed more power down the road. The OP has a good genny to get him out of any low power situations he may get himself in and that whole alternator idea just sounds like a can of worms to me.
2009 Jayco Eagle Superlite 25.5RKS
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bananadanna
Cambridge, MA
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The 250a alternator is too much.
I upgraded the 90a alternator on my Sprinter to 150a in order to feed a 420a-hr coach bank. I have a dc fridge and a 2000w inverter and a microwave and sundry small electronics. Daily power usage averages less than a kw-hr. Virtually all our camping is boondocking.
No solar or genset use needed if the van gets driven once every four days.
My relatively large bank accepts a kw-hr from the alternator very quickly, so even shortish errands restores an extra day of capacity.
I'd think two batteries would be fine if you're not running an electric kitchen like me. I get both long draws for the 18w average fridge and short heavy draws for the 1100w micro.
Solar can also displace alternator miles. I'd add some if I stayed still for a week or more. Or bring my genset along.
Dan
02 Freightliner Sprinter 2500 long tall home brew conversion
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Matt_Colie
Southeast Michigan
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DonMichUP wrote:Rich: What sort of trouble? The discharge state makes sense, but I'll be charging while driving as well as idling, and also charging while the generator is being used.
Don,
I used to run a business that did this sort of thing for cruising yachts. If you would like some particular information, contact me at info@southpointechandler.com. I can probably provide some specifics and helpful advice.
Have you figured out how you are going to separate the chassis and the house batteries and still charge both?
Matt
Matt & Mary Colie
A sailor and his bride and the black dog going to see some dry places in a coach made the year we married.
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mexbungalows
las peñas, michoacan, mexico
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Besides engineering battery manufacturing, I design (still active) automotive, marine and industrial alternators.
250 amps is too much to ask of a machine that will fit under your hood. Anyone can increase high speed power in an alternator by deleting turns in the stator and increasing wire diameter. All power increases come with a SEVERE degradation of amperage output at lower engine speeds.
It takes careful engineering to provide a product that performs satisfactorily in all crucial modes of operation. Anything more than @ 200 amperes is going to overtax your serpentine belt.
That's my two cents worth...
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pnichols
Santa Cruz Mountains
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Quote:250 amps is too much to ask of a machine that will fit under your hood
Well ... not exactly.
These units deliver way higher than the equivalent of 250 amps @ 12V, albeit at standard AC 60Hz 120V power. Note in their literature that they can be belt drive (under the hood) or tranny PTO driven. Also note in their literature that they say the approximate limit of 12V alternator power is 4KW ... which works out to well over 300 amps of 12V DC power as an upper limit:
http://www.aurasystems.com/pages/prod_intro.html
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